1. Field of the Invention
The present invention relates to motor drive technology, and in particular, to a motor drive device provided with a lock protection function, a cooling system using the motor drive device, and a lock protection method.
2. Description of the Related Art
With the speeding up of personal computers and workstations in recent years, operation speeds are increasing steadily for computational LSIs (Large Scale Integrated circuits), such as in CPUs (Central Processor Units), DSPs (Digital Signal Processors) and the like.
In such LSIs, as the operational speed, that is, clock frequency, increases, amounts of generated heat become large. There is a problem in that heat generated from an LSI leads to thermorunaway of the LSI itself, or has an effect on a surrounding circuit. Therefore, appropriate thermal cooling of the LSI is an extremely important technology.
An example of a technology for cooling the LSI is a cooling method of air-cooling by a cooling fan. In this method, for example, the cooling fan is installed opposite a front surface of the LSI, and cool air is blown on the LSI front surface by the cooling fan.
In a motor that drives the cooling fan, when the motor is locked by a foreign object being caught in the fan or the like, there is a risk of damaging device reliability by an excess current flowing in a coil or a semiconductor device. To tackle this type of problem, a lock protection circuit is used which stops energization of a motor coil when rotation of the motor is stopped.
In the technology described in Patent Document 1, when it is detected that rotation of a motor is stopped based on output of a rotation sensor that detects a rotation state of the motor, an automatic reset signal E is generated until the motor is reset to a rotation state. The automatic reset signal E is, for example, a signal that sequentially repeats an ON state of approximately 0.5 seconds and an OFF state of approximately 3 seconds. That is, when it is detected that rotation of the motor is stopped, after a halt period of approximately 3 seconds an attempt to start the motor for 0.5 seconds is repeated.
However, in the technology described in Patent Document 1, a lock protection function operates not only in cases in which the motor is locked, but also when rotation of the motor is stopped by an instruction by a control signal. As a result, when a signal that makes the motor rotate, from outside, is inputted, after operation of the lock protection function, after this input, until the automatic reset signal E is asserted, the motor cannot be rotated. That is, after the motor has been stopped by an instruction by the control signal, when a temperature rise of a device to be cooled is detected and the motor restarts rotation, a time lag until the start of rotation occurs, and there is a problem with temperature management.
Patent Document 1: Japanese Patent Application, Laid Open No. 2005-6405
Patent Document 2: Japanese Patent Application, Laid Open No. H10-234130